Unified description of early universe with bulk viscosity

Abstract

A class of homogeneous and isotropic zero-curvature Robertson-Walker models with bulk viscosity is studied. Solutions are obtained with the parameter gamma of the "gamma-law" equation of state p = (γ - 1)ρ in which the adiabatic parameter γ varies continuously as the universe expands. A unified description of the early evolution of the universe is presented with constant bulk viscosity and time-dependent bulk viscosity in which an inflationary period is followed by a radiation-dominated phase. We also establish the time dependence of the cosmological constant in terms of varying γ index. Some physical properties of the models are also discussed.